Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
2002-04-10
2004-10-19
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C162S263000, C162S252000, C162S259000, C162SDIG004, C700S128000
Reexamination Certificate
active
06805772
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 101 18 508.1, filed on Apr. 12, 2001, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a fibrous material web, in particular paper or cardboard web.
2. Discussion of Background Information
In the previously known apparatuses for paper manufacture, retention is determined on-line through the stock consistencies measured in the back water and in the stock feed to the headbox, and is kept constant through regulation of the retention agent quantity or quantities. A known paper apparatus with retention regulation of this nature is shown schematically in FIG.
1
.
This method based on a regulation of retention has, among other things, the disadvantage that formation becomes increasingly worse as retention becomes greater. To avoid poor formation, the retention must be set for the maximum possible retention with a large safety margin.
In this connection, formation is generally understood to mean the structure and degree of uniformity of fiber distribution in the fibrous material web, e.g. paper, either measured or evaluated, e.g. by light sent through. Formation is generally also referred to as the “look-through” of the fibrous material web or of the paper. Retention is understood to mean the proportion of the mass retained by the wire or wires relative to the total mass applied to the wire.
SUMMARY OF THE INVENTION
The present invention provides an improved method and an improved apparatus of the aforementioned type, in which the aforementioned disadvantages are eliminated.
In this regard, the invention provides a method for manufacturing a fibrous material web, in particular paper or cardboard web, in which the formation of the fibrous material web is measured on-line as a controlled variable and is maintained at a preselectable target level via an automatic formation regulator.
In this connection, the formation can be maintained at the preselectable target level in particular by appropriately changing the added quantity of at least one retention agent.
According to one preferred practical embodiment of the method in accordance with the invention, the retention is continually maintained at the respective maximum possible value.
In that two different retention agents are advantageously added at two different points (dual system), the retention can also be constantly maintained at a preselectable high level. Advantageously, the formation is maintained at the preselectable target level through appropriately changing the ratio of the added quantities of the two retention agents.
In this connection, formation regulation can be performed in various ways. A few possibilities are mentioned below purely by way of example.
Thus, for instance, formation can be set or regulated in that two retention agent mass flows Q
R1
, Q
R2
at a constant ratio Q
R1
/Q
R2
are changed appropriately, or increased or reduced.
Another possibility includes, for example, that the formation is measured, the measured value is compared to a target value, the added quantity of a first retention agent of a dual system is adjusted appropriately to match the formation to the target value, and in order to set the highest possible level of retention the added quantity of a second retention agent of the dual system, or the ratio between the added quantities of the two retention agents, is corrected up to the point where the formation begins to worsen again.
Moreover, it is possible, for example, to superimpose the formation regulation on a retention regulation. In this connection the retention regulation, which can be accomplished in a conventional manner, can in particular be faster than the formation regulation.
The two different retention agents can, for example, include polymers with different charge densities (anionic/cationic) and/or different molecular weights. In this connection, the two different retention agents can include, e.g., polyethylene imine (PEI) and polyacrylamide (PAM).
In accordance with another practical embodiment of the method in accordance with the invention, the first retention agent includes a polymer, e.g. polyacrylamide, and the second retention agent includes inorganic microparticles, e.g. bentonite, hydrocol, etc. Thus, for example, one polymer can be provided for coarse flocculation and one agent for fine flocculation.
In certain cases, it is advantageous if raw material influences and/or the water flow in the wet section are also included in formation regulation. This is possible through the use of fuzzy logic and/or predictive controls, in particular.
Thus, for example, when short-fibered raw materials are used, the formation is worsened to a lesser extent with increasing retention than when long-fibered materials are employed.
This material-dependent relationship between formation and retention can be taken into account in the control algorithm. This can be accomplished, for example, within the framework of a formation regulation superimposed over a retention regulation, or in that the ratio Q
R1
/Q
R2
of the mass flows of the retention agents of the dual system are also selected by fiber type (raw material type).
The apparatus in accordance with the invention for manufacturing a fibrous material web, in particular paper or cardboard web, accordingly includes an automatic formation regulator in which the formation of the fibrous material web is measured on-line as a controlled variable and is maintained at a preselectable target level.
The present invention is directed to a process for manufacturing a fibrous material web in an apparatus having an automatic formation regulator. The process includes on-line measuring of formation of the fibrous material web, utilizing the on-line measured formation as a controlled variable, and maintaining the formation at a preselectable target level via the automatic formation regulator.
According to a feature of the instant invention, the fibrous material web can include one of a paper or cardboard web.
In accordance with another feature of the invention, the formation can be maintained at the preselectable target level by changing an added quantity of at least one retention agent.
The process can further include continually maintaining retention at a maximum possible value.
Further, different retention agents may be added at different points, and the process can further include adjusting the retention. The two different retention agents may include polyethylene imine (PEI) and polyacrylamide (PAM).
Moreover, two different retention agents can be added at two different points, and the process may further include constantly maintaining the retention at a preselectable high level.
According to still another feature of the invention, two different retention agents may be added at two different points, and the process can further include maintaining the formation at the preselectable target level by changing a ratio of added quantities of the two different retention agents.
In accordance with another feature of the present invention, two different retention agents can be added at two different points, and the two different retention agents may include polymers with at least one of different charge densities and different molecular weights. The different charge densities may include anionic/cationic differences.
The process can further include one of adjusting or regulating the formation by one of increasing and decreasing a constant ratio Q
R1
/Q
R2
, wherein Q
R1
and Q
R2
represent retention agent mass flows.
After the on-line measurement of the formation, the process may further include comparing the measured value to a target value, adjusting an added quantity of a first retention agent of a dual system to match the formation to the target value, and correcting one of an added quantity of a second retention agent and a ratio between the added quantit
Greenblum & Bernstein P.L.C.
Griffin Steven P.
Hug Eric
Voith Paper Patent GmbH
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